Compared with flow-pressing, in which the deformation force acts simultaneously on the entire workpiece surface, in the case of wobble-die forging, force is as is known exerted only on a partial surface, so that only a small amount of friction can arise and the material flows in a radial direction without great resistance. For this, the blank is deformed between upper die and a lower die with circularly rocking movement of the upper die, wherein the deformation force is concentrated on only a partial surface of the workpiece. The deformation is effected by movement of the pressure zone over the entire workpiece surface.
Due to the smaller contact area and the more favorable friction conditions, the deformation force in wobble-die forging machines is thus substantially smaller than in the case of conventional flow-pressing.
Resulting from this are the advantages of appreciably smaller machines, less die loading and smaller noise development. In addition, products significantly larger in shape can be attained in one operating step by the wobble-die forging machines by comparison with the multistage dies necessary for large products in conventional flow presses, with all their costs and setting-up times.
Thus wobble-die forging has become more significant, particularly since the technologies required for it have in recent times been elaborated to the point that functionally capable machines for the purpose are now available.
However, some functional means of the existing overall conceptions require further improvements.
Thus, for example, the construction and drive of the eccentric sleeves, which engage the guide spigot of the bell-shaped upper die mounting, for producing different kinds of movement at the upper die, have problems.
Although the means hitherto used for this already permit a circular movement of the upper die for circularly symmetrical deformations, a spiral movement for radial and axial deformation, a rectilinear movement for deformations in two directions as well as a multi-lobe curvilinear movement for deformations of parts with pronounced surface structure, these means are very expensive, cannot be fully controlled and are very large size.
The reason for this is inter alia the co-axial guidance of drive axles, of which each is rotationally connected with a respective one of the eccentric sleeves. Both axles in that case end in a gear rim, through which each eccentric sleeve is in driving connection with a regulable direct current motor and through which on the other hand both of the eccentric sleeves are operatively connected through an expensive transmission gear.